Technical Abstract:
During the periparturient period, the dairy cow experiences a state of natural immunosuppression that is associated with heightened susceptibility to infectious disease. During this period, alterations in T cell percentages in the circulation parallel a reduction in functional capacities of peripheral blood mononuclear cell (PBMC) population. Hormonal and metabolic demands of pregnancy and lactation as well as the physiologic stress of calving likely contribute to periparturient immunosuppression. Objectives of this study were to evaluate the phenotype and functional capacities of PBMC populations in periparturient cows, and, secondly, determine whether changes in composition and function could be, in part, attributable to the presence of a functional mammary gland. Ten mastectomized and eight intact multiparous Jersey cows (six for each for functional study) were used. Using monoclonal antibodies against T-cell subsets, the B-cell, and the monocyte, the composition of PBMC populations was characterized by flow cytometry. For the analyses, cells were obtained several times a week from '4 wk prepartum to 4 wk postpartum. Functionality of PBMC populations was assessed by assays measuring mitogen-induced lymphocyte proliferation, IgM secretion, and IFN-gamma secretion. Cells used in these assays were collected twice weekly from '3 wk prepartum to 3 wk postpartum. Percentages of CD3+, CD4+, CD8+, and gamma/delta TCR+ cells in intact cows decreased progressively with the approach of parturition, while monocyte percentages increased. Synthesis of DNA and secretion of IFN-gamma and IgM by mitogen-stimulated intact-cow PBMC were lowest around the time of calving. In contrast, compositional and functional changes in PBMC populations from mastectomized cows were minimal or absent at these times. Regression analysis revealed significant associations between composition and functional capacity of the PBMC population. These results indicate that the mammary gland and metabolic stresses associated with lactation contribute to the generalized immunosuppression affecting dairy cows during the periparturient period.